Sorry, but we have no automation for updating previous versions.
If you don't want to install PHPMyWebHosting completely new, you must manually insert install/update.sql into your database.
Do this by using PHPMyAdmin or the command line tool mysql by
mysql -u $USER -p$PASSWORD $DATABASE < install/update.sql
Export the entries from table apache, remove CREATE definition and replace "apache" with "domains".
Also change in database "mysql", table "table_priv" apache to domain.
Then edit /etc/apache/httpd.conf and change SQL-Query from "apache" to "domains".